Hfc k understanding bi-direction


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Hfc k understanding bi-direction

  1. 1. Broadband System - K Satellites are spaced every 2nd degrees above earth"C" BandToward satellite 6.0 GHz "L" BandToward earth 4.0 GHz Toward satellite 14.0 GHz Toward earth 12.0 GHz TV TRANSMITTER Headend Cable area 1 Bi-Directionality on a Broadband System.
  2. 2. Understanding Bi-directional Operation on a HFC System 2
  3. 3. Bi-Directionality on a Broadband System.Since a HFC system is a bi-directional operating system, thefrequency allocations are:•From Headend to the Subscribers : 50 to 750, 870, or 1,000 MHz•From the Subscribers to the Headend : 5 to 40, 42 or 65 MHz•We now are starting to see: 5 to 65 MHz for return freq.•And forward frequency from: 85 to 870 or 1,000 MHz 3
  4. 4. Bi-Directionality on a Broadband System.A Broadband HFC Communication system utilized two types of communications technology:• Fiber optic technology is used to transport signal for the long distance. Usually one fiber transmits forward signal (50-870 MHz from the Headend to a Optical Node and one more fiber transmits return signal (5 - 40 MHz) from a Node to the Headend.• Coaxial cable is used from the NODE and it is transmitting in both directions (50-870 / 5-40 MHz), from the Optical Node to the each subscribers.• The OPTICAL NODE, transfers Light Signal, coming from the Headend, to Electrical Signal (RF and Digital), sending these signals to each subscribers by coaxial cable.• The OPTICAL NODE, also Transfers Electrical Signal (RF and Digital) from all the customers to light signal, sending them to the Headend. 4
  5. 5. Bi-Directionality on a Broadband System.All optical NODE must be equipped with a Photo diode on theforward path, a bi-directional filter at each output of the coaxialsystem to permit an HFC system to operate in a bi-directional wayand a return Laser to transmit return signal toward the headend. Photo diode RF Amp. Fibre 50 - 1,000 MHz Bi-Directionnel 5-40 / 50-1,000 MHz 50- Filtrer Fibre 5 - 40 MHz Coaxial Cable LASER 5
  6. 6. Bi-Directionality on a Broadband System. All RF amplifier must be equipped with a bi-directional filter at each input and outputs to permit an HFC system to operate in a bi-directional way. Section RF Section RF 50 - 1,000 MHz 50 - 1,000 MHz Bi-Directionnal Bi-Directionnal5-40 / 50-1,000 MHz 5-40 / 50-1,000 MHz Filter FilterCoaxial Cable Coaxial Câble Section RF Section RF 5 - 40 MHz 5 - 40 MHz 6
  7. 7. Optical NODE.Light 50-870 MHz 50- 50-870 MHz 50- Coaxial Cable Light 5-40 MHz 5- 5-40 MHz Fiber Optic RF section Optical receiver Optical Transmitter 50-870 MHz 50- 5-40 MHz 7
  8. 8. Determining the Required Operating Level of the Return System.•Because the return path on a Broadband system works on a conceptof UNITY GAIN, the system need to determine the required ReturnInput Level at each active equipment (Amplifier and Node).•That return Input level need to be at the output of the housing.•That Return Input LEVEL is usually between : 15 to 20 dBmV 5-40 50-870 5-40 MHz MHz 5-40 MHz MHz RF Amp. 27 Signal from customer 5 MHz 40 15 or 20 dBmV DOCSIS Signal Return Input 8
  9. 9. Operating Level of the Return System.Once the operating level is determine, it is also very important touse the output test point to introduce the signal from theRETURN TRANSMITTING EQUIPMENT used for this operation.The actual level at the input of the return amplifier will changedepending on the type of amplifier utilised. These amplifiers canbe Line Extender, Mini-Bridger and Distribution amplifiers Return TX Equipment Test Test Point Point 50-870 MHz H H 27 L L Signal from customer 5 MHz 40 Test 15 or 20 dBmV Test Status Point Monitoring Point DOCSIS Signal 5-40 MHz EQ RF Amp. JXP Attenuator Return input level 9
  10. 10. Operating Level of the Return System.After the HFC system has been aligned in both direction, each Cablemodem outputmust be adjusted, to hit a + 15.0 or + 20.0 dBmV at each input housing of all theNODE or RF Amplifiers on the HFC system. This is done automatically by DOCSISoperating system. 10
  11. 11. Unity Gain.•Unity Gain, basically means output @ 1 and output @ 2 willhave a different gain and slope, to fit in the required Input @ 3•Each amplifier need to be adjusted locally, to hit the properlevel at the node or the amplifier at location @ 3*= Where return amplifier are adjusted 11
  12. 12. The Fiber Optic Section.The fiber optic section, on a HFC system, is a flat operatingsystem, in both, the forward and the reverse section. 12
  13. 13. The Coaxial Cable Section.The loss of signal, in the coaxial section, works differently then fiberoptic section, as frequency increase, signal loss also increase. The slope response must be constant, The forward and return response slope on on this side of all the amplifier, for the this side of the amplifier, depends on the forward section (50/870 MHz) as for the length of cable and the loss of the passive return section (5/40-42 MHz) (5/40- equipment, placed between the previous amplifier 13
  14. 14. Adjusting the Return Signal on a Broadband System.Adjusting the forward section, is something, technician have been doing for year. Adjusting the reverse system is quite different, it either requires: • Two technicians communicating, to properly adjust the return amplifier. • 2 or 4 Modulators to be transported at each amplifier, a Spectrum Analyzer at the Headend, connected to a Modulator, and a TV set at each amplifier. • Or the use specialized equipment, We need to adjust the Gain and Slope of the return amplifier at 1 to have the proper input signal level at: 2 14
  15. 15. Adjusting the Return Signal on a Broadband System. Return signal provided by return sweep equipmentAfter you have decided the right RETURN input level (15 dBmV in most cases),you need to add the test point loss and begin adjusting the return system. 15
  16. 16. Adjusting the Return Signal on a Broadband System.•When we adjust the return section of a HFC system, you must remember thatyou need to install a RETUN EQ and RETURN PAD, so you can hit the rightreturn level at the following amplifier or node.•These EQ and PAD goes on the left of the return amplifier, toward the nextamplifier or optical node.•The EQ is for setting the proper slope, which should be flat at the next ampifier•The PAD, is for setting right input level at the next amplifier. Return EQ Return 1 PAD Return 2 In some instance this could be a thermal PAD Could be 1, 2 3 or 4 return input 16
  17. 17. Adjusting the Return Signal on a Broadband System. 8 Return signals +35 dBmV Between 5 & 42 MHz with a -20 dB test point Optical NODE The amplitude of 8 signals are transmitted in FSK with also the INGRESS level between 50-52 MHz or 72-75 MHz 50- 72- 0 dBm CMTS Carrier LevelHeadend from Headend 9581-SST 9581- Signal Optical Equipments INGRESS from Headend Optical Interconnection 17
  18. 18. Adjusting the Return Signal on a Broadband System. Return RF level at headend INGRESS level at headendAbove is the picture of the eight (8) signals been sent from the input of the returnsignal. The bottom section one show the ingress on the return signal been tested.Both of these information are read in the forward path of the HFC system. 18
  19. 19. The Return Signal on a Line Extender.Signal loss between the return input and the input at the Return IC : 1.5 dB for H/L coupler. 1.5 dB thru 20 dB test point 1.5 dB for return input Status monitoring Total : 4.5 dB 19
  20. 20. The Return Signal on a Mini-Bridger.Signal loss between the return input and the input at the Return IC : 1.5 dB for H/L coupler. 1.5 dB thru 20 dB test point 4.5 dB for splitter 1.5 dB for return input Status monitoring Total : 9.0 dB 20
  21. 21. The Return Signal on a High Gain Amplifier.Signal loss between the return input and the input at the Return IC : 1.5 dB for H/L coupler. 1.5 dB thru 20 dB test point 4.5 dB for splitter 4.5 dB for 2nd splitter 1.5 dB for return input Status monitoring 21 Total : 14.5 dB
  22. 22. Difference in Response Between a 20 and 30 dB Test Point. 22
  23. 23. Amplifier Equipped with 30 dB High Impedance Test Point. With amplifiers equipped with high impedance, 30 dB test point, I strongly recommend installing a 20 dB multitap, at each output of the amplifiers, that way you will get a truer reading when adjusting the forward and the return path. 23
  24. 24. Signal Loss Between 2 Different Return Path. Example of gain required for return signal Cable TX-625Loss at : 860 MHz 1.94 dB/100Loss at : 5 MHz 0.13 dB/100Loss at : 40 MHz 0.38 dB/100 Input amplifier, Input amplifier, Ch : 5 15.00 dBmV Distance amplifier 1 - 2 Ch : 5 15.00 dBmV Ch : 40 15.00 dBmV 1550 ft Ch : 40 15.00 dBmV 31.07 dB / 860 MHz 1 2 Headend -1 dB 5.89 dB / 40 MHz H H H H L L L L Ch : 5 40.00 dBmV -12 dBCh : 40 40.00 dBmV H Distance amplifier 1 - 3 H L L 800 ft 27.52 dB / 860 MHz Gain at: 5 MHz 29.50 dB 3.04 dB / 40 MHz Gain at: 5 MHz 18.02 dB Gain at: 40 MHz 29.50 dB Gain at: 40 MHz 21.89 dB 3 In général Return Opt. Tx H H Input amplifier, L L requires around + 35 dBmV Ch : 5 15.00 dBmV input for proper operation. H Ch : 40 15.00 dBmV Required output L Level for the next amp. Gain at: 5 MHz 28.04 dB Gain at: 40 MHz 30.04 dB Required output Level for the next amp. 24
  25. 25. Sequence for Adjusting the Return Path.For the return path, the system should be adjusted in the following sequence. Return Set-in up sequence; 1. From Node to Headend 2. From Amp. 1 to Node 3. From Amp. 2 to Amp. 1 4. From Amp. 3 to Amp. 2 5. From Amp.4 to Amp. 3 25
  26. 26. Multi wavelength return frequencies.Return ReturnOptic Optic RX TX 8 8 7 7 Single fiber optic with 8 “CWDM” frequencies 6 6 5 5 4 4 3 3 2 2 With CWDM technology, it is now 1 1 possible to have 8 return laser transmitting on one fiber. CWDM CWDM 26
  27. 27. Multi wavelength return frequencies. 8 7 6 5 Opt.Return RX 8 4 7 6 5 Each optical coupler will require a 3 different value, so all light levels will 4 be within a 2 dB in level 3 Each return laser will also required the right wavelength frequency. 2 2 1 1 27
  28. 28. Multi wavelength return frequencies.-6.44 -6.86 -6.95 dBm CWDM The loss of each return TX will be: 8.0 dB 2.64 dB 3 1= 3.0 -(3.63 - 3.2 - 1.43- 1.8 - 8.0) = -6.95 dBm6.8 dB1.8 dB 3 dBm 4.0 km 2= 3.0 -(4.1 - 4.0 - 1.8 - 8.0 ) = 6.86 dBm 1.43 dB loss4.1 dB 23.2 dB 3 dBm 3= 3.0 -(6.8 - 8.0 ) = 6.95 When using CWDM technology, we should 11 km try to keep all of the light level within 1.5 dB 3.63 dB loss from each other. The thru loss of the CWDM is not calculated 1 3 dBm 28
  29. 29. Signal Loss Between Two Cable Modem.Loss of signal between Cablemodem and Input of the return amplifier. As we go further away from the amplifier, the signal loss between the Cablemodem and the amplifier get smaller, this will shown in the next presentation. 29
  30. 30. Actual Level Required at Each Cable Modem for Proper Operation. Actual level in dBmV, required out of the Cablemodem, to hit proper input at the next amplifier or Optical Node, where the forward signal output is : 14 dBmV at 750 MHz Cable P-III-625 INPUT @ 870 MHz OUTPUT 34 - 46 Forward output + 14.0 dBmV @ 870 MHz 17.95 dVmV dBmV 100 100 100 100 100 100 100 29 29 26 23 20 15.5 10 15 dBmV - 1.37 - 1.37 - 1.37 dB dB dB QAM TV TV TV Cablemodem - 7.0 Cablemodem Cablemodem - 7.0 - 7.0 5 MHz 40 dB dB Output dB Output Output 52.37 dBmV 48.44 dBmV 43.02 dBmV Signal required out of each Cablemodem, to hit the proper required 15 dBmV at the input at the housing This actually shows why new Cablemodem are now equipped with a output level control. This output level is controlled by the CMTS or the SERVER located in the headend. 30
  31. 31. A Bi-Directional Operating System. Fiber opticHE RING Reverse Path from caller From server to call Response from call From server to caller IP Telephone call or Cable modem Start from here. Hi….. 31
  32. 32. A Bi-Directional Operating System.•You’ll now see a short PC Video demonstration a HFC return signal. Pattern of the Video Recording of the return signal: •19:30:25 5 to 50 MHz upstream system. •19:30:25 3 active cable modem carriers (3.2 MHz DOCSIS) •19:31:10 Ingress appear between 5 to 18.5 MHz. •19:31:18 Ingress grows substantially stronger. •19:31:30 Ingress disappear. •19:31:33 Common path distortion (CPD) appears. •19:31:41 Common path distortion grows very severely. •19:31:51 Common path distortion goes away. •19:32:15 All traffic is now OK. •19:32:34 Analyzer a ZERO SPAN, centre frequency at 41 MHz •19:32:52 Noise floor rises to about 15 dB C/N. •19:32:52 Interference disappears, Noise floor back to 30 dB C/N •19:33:57 Analyzer is brought back to frequency domain mode. mode. •19:34:27 End of recording. 32
  33. 33. A Bi-Directional Operating System.Controlling INGRESS is possible by utilising a device called ClearPath. AClearPath is a return switch that locate the source of INGRESS in a HFCsystem. To determine where the ingress is located, the ClearPathselectively switches a 6 dB pad into the return path. In locations where theingress is severe, the ClearPath can also switch off the entire upstreamband until the ingress sources in repaired. Technical specifications: •90 volts, 15 amp power passing •Smooth, non-disturbing switching •Switching time 10 ms •Surge protected •Provides temporary release for severe ingress •Single agile FSK carrier 33
  34. 34. A Bi-Directional Operating System. Controlling INGRESS A1. With INGRESS coming from section A and the return path without ingress control, the return system might not been operational. If ClearPath-4 is installed, and with a ( 6 or 40 dB attenuation Pad ) operating, the rest of the return path becomes fully operational.2. The ClearPath can be controlled by using a simple software and a spectrum analyzer or a complete software, that will activate the proper ClearPath, activate the attenuation Pad and give the proper location. 34
  35. 35. A Bi-Directional Operating System. Controlling INGRESS•TraffiControl is a powerful new feature for Trilithic Reverse Path Maintenance System. PathThis system can not only detect INGRESS hiding inside your return services, it can returnscan your return system and detect excessive ingress, logs the event, generates event,alarms and takes other programmed actions, like finding where the problem occur by theopening and closing and selecting the proper ClearPath.•TraffiControl can also select the operating section of the return path and forget about returnthe none occupied section, as shown above. 35
  36. 36. A Bi-Directional Operating System. Controlling INGRESS Ingress SwitchWith newer optical NODE and RF amplifier,it is now possible to install INGRESSSwitch inside the amplifier and controlsINGRESS. This INGRESS switch is capableof inserting a 6 dB PAD or a 40 dB PAD atdistance. The 6 dB PAD help us locate theproblem area and the 40 dB PAD removefrom the return system the problem area.. 36
  37. 37. A Bi-Directional Operating System. Controlling INGRESS•One other way to controlled and look for INGRESS, is by using a 9581-SST and 9581-9581-SSR. You then go to any amplifier, get the return signal from the 20 dB test9581- thepoint and look at the ingress at the 9581-SST at the Headend. By removing 9581-attenuator PAD before the return IC you can actually tell where the INGRESS iscoming form.•The problems with this solution, every time you remove a PAD from the return fromsystem, you actually stop the return system to operate and you will also have to willmove from amplifier to amplifier, before you can locate the problem area. problem 37
  38. 38. A Bi-Directional Operating System. Controlling INGRESSPressinghere willintroduces a 6 This return REVERSE TEST PROBE can also help locatingdB PAD INGRESS. By pressing a control, a 6 dB pas will be introduce to the return system and let you know if you have located the ingress or if the ingress is coming from somewhere else. 38
  39. 39. A Bi-Directional Operating System.It is also possible to read return INGRESS and CPD on the return system with the use of a spectrum analyzer. Return system with INGRESS. Return system without INGRESS. 39
  40. 40. A Bi-Directional Operating System. Adjusting a return system in the field. 40
  41. 41. A Bi-Directional Operating System. Controlling INGRESSOne other good way to removed INGRESS on a bi-directionalsystem, is to install a High Pass Filter at each location where bi-directional signal are not required. 41
  42. 42. A Bi-Directional Operating System. Controlling INGRESSWith some systems operating a VIDEO on DEMAND or a PAYTV System, you should installed a INGRESS control unit withthe capacity of talking to the controls units installed at eachcustomer with these services. These controls units are usuallyrequiring a frequency between 9 to 10 MHz 42
  43. 43. A Bi-Directional Operating System. Testing return signal, from the home to the headend.Some equipment can test thequality of the return signal. Theseequipments send signal to aheadend equipment, thisequipment does some calculationand send you the result on theforward path.The picture show 8 frequenciesfrom 5 to 42 MHz been sent fromthe home to the headend. Theheadend piece does some C/Ncalculation and let you if thesystem meet the returnrequirement.This system send the following frequencies at the headend: 5.5, 13, 18,24, 27, 30, 34, and 39.6 MHz. The level received at the headend is around25 dBmV. The highest INGRESS level been around –25 dBmV, where theC/N of each of those frequencies are between; 42 to 36 dB C/N. 43
  44. 44. A Bi-Directional Operating System. Controlling INGRESSA High Pass Filter installed at each home, not requiring by-directional communication , will help the system control his ingress problem. 44
  45. 45. Test! 45
  46. 46. •What is a proper return level at the input of an RF amplifier?_____________________________________________________________•In what direction do we line-up the return system on a HFC system? line-______________________________________________________________•What happen to return RF signal at the NODE?______________________________________________________________•How many return signal do we generally combined at the headend?_______________________________________________________________•Are all the cable modem adjusted at the same level at the customer? customer?_______________________________________________________________•What type of modulation is generally used for cable modem?_______________________________________________________________•Where is the return equalizer situated on the RF section of an amplifier? amplifier?_______________________________________________________________•What is called the none wanted signal, that can actually stop the return system to work? the_______________________________________________________________ 46
  47. 47. 47